What is scaling? (Pertaining to water systems)?
Answer:
Scale is when (mostly) inorganic substances precipitate out of water onto the sufaces of pipes, pumps etc. Most common scale in the house is the hard deposit which forms in kettles in hard water areas and the limestone scale which can form in the toilet bowl. In engineering, scaling causes loss of perfomance in the system and has to be controlled either chemically though additives as used in industrial water boilers or physically as used for example in the oil industry to "pig" the pipes basically by blasting a mechanical plug down the pipe to clean the system.
*Scaling is the development of hard and adhesive deposits on hot surfaces, by precipitation of salts which solubility varies in the opposite of temperature.
These salts are mainly calcium and magnesium carbonates derived from the thermal decomposition of corresponding bicarbonates, widely present in natural waters. Analysis of (M) Alkalinity let people be aware of the bicarbonate hardness liable to form carbonate scale.
Sulfate scale is made with calcium sulfate which solubility decreases when temperature increases. Hard and adhesive , it causes heat transfer losses more important than carbonate scale.
Constituted by silica, the siliceous scale is very hard and very adhesive with occasionally a glassy appearance. It is responsible for very high heat transfer losses (75% for 0.1 mm thickness).
*Water used into heating or cooling systems, whether from drilling, spring or surface, comes from the nature where it fills itself with minerals, dissolved gas and living micro-organisms.
Dissolved mineral salts will increase electrical conductivity and so the corrosivity (chlorides, sulfates), calcium and magnesium will influence the hardness and cause scaling and mudding off phenomena, silica by covering hot walls of installations will be harmful to heat exchanges.
Dissolved gas, especially oxygen and carbon dioxide will generate corrosion or scaling.
*So, it is imperative to treat these scales by proper chemicals periodically.
Or else you have to go for water softening plant.
Salts less water is extremely important for boilers and water cooled jacketed equipments.
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Water used in industry for the production of steam etc.., does cause some major problems when heated. For example: -
*..Bi-carbonates, when heated, will break down to form insoluble carbonates which give rise to deposits of scale or
'fur' inside kettles and piping. This build up of layers of scale will cause poor heat transfer and the heating element can overheat and burn out or, in the case of a steam generation boiler, can cause pipe blockages.
The kind of hardness caused by the bi-carbonates of calcium and Magnesium, is called 'Temporary Hardness', as boiling removes the chemicals concerned.
*...Calcium sulphate has 'Inverted Solubility' - as water temperature increases, the solubility of the sulphate decreases causing crystals to form that build up into
scale deposits. Scale build up can also cause blockage of piping which will result in plant shut down for cleaning of the equipment.
*...The chlorides, sulphates and nitrates of Calcium and Magnesium cause what is termed 'Permanent Hardness' in water.
These are removable by special 'Water Treatment' techniques. (Notes on this are available if required).
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